1. Field of the Invention
The present invention relates to a semiconductor memory device and method for testing same, and more particularly it relates to a semiconductor memory device having a disturb test function and a method for testing such a semiconductor memory device.
2. Related Art
Of the causes of failures in DRAMs, failures occurring at the time of sensing account for a large proportion, and are difficult to discern. Several causes of failures that can be cited are failure in the capacitance of a cell capacitor, charge leakage from a cell capacitor, decrease in the initial signal amount at the time of sense starting caused by sluggish operation of a word line, sense operation delay caused by insufficient capacity of a sense amplifier, erroneous sensing caused by a large high/low variation (unbalance) in sense amplifiers, and disturbance from a neighboring bit line or the like. In performing a shipping inspection, it is necessary to perform test patterns accommodating all of the above-noted causes for every memory cell, and with the increase in memory capacities and shrinking of memory design rules, the amount of time required for such testing is constantly increasing. Additionally, because of the difficulty in discerning failure factors, it is difficult to provide feedback of failure countermeasures to the manufacturing processes. The present invention enables the performance of testing separated from such problems as insufficient capacity of a sense amplifier, and large variations, and by doing so simplifies the distinguishing of failure factors, so that it is possible to provide quick feedback to the manufacturing processes. In addition, by performing a test in accordance with the present invention, it is possible to eliminate failures related to a sense amplifier from combinations of various failure factors, thereby enabling simplification of the test patterns, which shortens the testing time.
The Japanese Unexamined Patent Publication (KOKAI) No. 2001-35197 shows the semiconductor memory device having disturb test function. The above-mentioned publication does not shows disturb test performed for sense amplifiers.
An object of the present invention is to improve the above-noted drawbacks of the prior art and to provide a novel semiconductor memory device which enables testing of sense amplifiers when a disturb test is performed and to provide a method for testing same.
Another object of the present invention is that by performing disturb test on the sense amplifiers, sense amplifier problems are eliminated, thereby enabling simplification of the test patterns, which shortens the testing time.